This invention relates to an apparatus and method for the treatment of benign prostatic hyperplasia (BPH), prostate cancer, and other diseases by application of focussed ultrasonic energy from a probe placed near the site of the lesion.
BPH is a very common disease in men over 50 years of age, in which swelling of the prostate results in obstruction of the urethra and consequent inability or difficulty in urinating. In its early stages it causes discomfort and inconvenience. Permitted to progress, it can result in severe pain and serious consequences. It is traditionally treated by transurethral resection of the prostate (TURP), a surgical procedure with good effectiveness but an unfortunate level of pain, blood loss, morbidity, complications, expense, lost time, and in some cases death. Other methods, using lasers or radio frequency or microwave energy, have not been proved to approach TURP in effectiveness. A method combining high effectiveness with fewer short-term bad effects than TURP is still urgently required.
Prostate cancer is the second leading cause of cancer-related death in men. In its early stages it can be treated successfully by radical prostatectomy, but this procedure has all of the disadvantages of TURP and in addition often results in incontinence, impotence, or both. Prostate cancer can also be treated by radiation therapy, but similar serious side effects are common if a sufficient dose is used to have a good chance of a favorable result. A curative method with less initial trauma is needed. More advanced prostate cancer is also treated by radical prostatectomy or radiation therapy, but this procedure usually does not result in cure, though it may achieve palliation. Since less is accomplished in these cases, a less invasive method is even more necessary.
Ultrasound is well known to urologists for its ability to image a volume of tissue, creating pictorial slices without the need to cut. It can do this because ultrasonic waves are transmitted through tissue without being too strongly attenuated, yet, because there is significant absorption by tissue, intense ultrasound can produce very substantial heating in the interior of an organ. The goal in exploiting this effect is to create a large ultrasound intensity at the interior region to be treated while minimizing the ultrasound intensity in tissue that is to be spared. Prior attempts have been made to use the capabilities of focussed ultrasound for treatment of BPH and prostate cancer. One approach utilizes extracorporeal ultrasound focussed from outside the body; another uses a transrectal probe.
U.S. Pat. No. 5,344,435, to Turner et al. describes the transurethral application of unfocussed ultrasound energy for the treatment of prostatic disease. The disclosed apparatus, however, does not exploit the ability of ultrasound to reach a focus within the tissue, and thus to deliver a higher intensity at an internal point than is present at the urethral wall. Accordingly, and despite the use of urethral cooling, the inventors do not recommend temperatures greater than 48.degree. C. Use of these temperatures diffusely in the prostate may be of some clinical value, but does not produce effects comparable to application of higher temperatures in a sharply defined volume of tissue, as taught in the present invention.
The apparatus of Turner et al. '435 operates in what is generally termed a hyperthermal mode. Energy transfer utilizing the apparatus of Turner et al. '435 is by radiation, that is, energy is transmitted from a source within the apparatus into a treatment volume much larger than the source itself. As a consequence of the hyperthermal irradiation temperature being limited to a maximum of 48.degree. C., the diseased prostatic tissue must be irradiated for relatively long periods of time, often up to 60 minutes or more. This is disadvantageous in that it requires the patient to be immobilized during such lengthy treatment sessions.
When a transrectal probe is used, the ultrasound must pass through 4 cm or more of healthy tissue before reaching the tissue that is to be destroyed. If the probe is outside the body, the ultrasound must pass through an even greater depth of healthy tissue. In either case, the large distance between the probe and the tissue to be treated is disadvantageous because it increases the difficulty of targeting the ultrasound accurately, because healthy tissue is exposed to the potentially damaging effects of high intensity ultrasound, and because a higher initial power must be used to make up for attenuation in tissue between the probe and the target.
A further drawback to prior systems is that they focus the ultrasound at peak intensity on each individual volume of tissue to be treated. This requires extremely accurate targeting, generally requiring an elaborate and costly targeting system such as diagnostic ultrasound. It further requires the provision of accurate relative motion between the probe and the patient. Because of the high power required to compensate for or attenuation, and because of the accurate targeting required, prior art systems are extremely expensive, costing well over one hundred thousand dollars and in some cases many times more.